Definition 6.13  See [1]}.) 
 Referring to Lemma REF , we call \(\lbrace \varphi _i\rbrace _{i=1}^d\) 
the first split sequence of \(\Phi \) .
Let \(\lbrace \phi _i\rbrace _{i=1}^d\)  denote the first split sequence of \(\Phi ^\Downarrow \) .
We call \(\lbrace \phi _i\rbrace _{i=1}^d\)  the second split sequence of \(\Phi \) .

